const PI = 3.14159265358979324
const x_pi = 3.14159265358979324 * 3000.0 / 180.0

export function delta(lat, lng) {
  // Krasovsky 1940
  //
  // a = 6378245.0, 1/f = 298.3
  // b = a * (1 - f)
  // ee = (a^2 - b^2) / a^2;
  const a = 6378245.0 //  a: 卫星椭球坐标投影到平面地图坐标系的投影因子。
  const ee = 0.00669342162296594323 //  ee: 椭球的偏心率。
  let dLat = transformLat(lng - 105.0, lat - 35.0)
  let dLng = transformLng(lng - 105.0, lat - 35.0)
  const radLat = lat / 180.0 * PI
  let magic = Math.sin(radLat)
  magic = 1 - ee * magic * magic
  const sqrtMagic = Math.sqrt(magic)
  dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) * PI)
  dLng = (dLng * 180.0) / (a / sqrtMagic * Math.cos(radLat) * PI)
  return { 'lat': dLat, 'lng': dLng }
}

// WGS-84 to GCJ-02
export function gcj_encrypt(wgsLat, wgsLng) {
  if (outOfChina(wgsLat, wgsLng)) {
    return { 'lat': wgsLat, 'lng': wgsLng }
  }

  const d = delta(wgsLat, wgsLng)
  return { 'lat': wgsLat + d.lat, 'lng': wgsLng + d.lng }
}

// GCJ-02 to WGS-84
export function gcj_decrypt(gcjLat, gcjLng) {
  if (outOfChina(gcjLat, gcjLng)) {
    return { 'lat': gcjLat, 'lng': gcjLng }
  }

  const d = delta(gcjLat, gcjLng)
  return { 'lat': gcjLat - d.lat, 'lng': gcjLng - d.lng }
}

// GCJ-02 to WGS-84 exactly
export function gcj_decrypt_exact(gcjLat, gcjLng) {
  const initDelta = 0.01
  const threshold = 0.000000001
  let dLat = initDelta
  let dLng = initDelta
  let mLat = gcjLat - dLat
  let mLng = gcjLng - dLng
  let pLat = gcjLat + dLat
  let pLng = gcjLng + dLng
  let wgsLat
  let wgsLng
  let i = 0
  while (1) {
    wgsLat = (mLat + pLat) / 2
    wgsLng = (mLng + pLng) / 2
    const tmp = gcj_encrypt(wgsLat, wgsLng)
    dLat = tmp.lat - gcjLat
    dLng = tmp.lng - gcjLng
    if ((Math.abs(dLat) < threshold) && (Math.abs(dLng) < threshold)) {
      break
    }

    if (dLat > 0) {
      pLat = wgsLat
    } else {
      mLat = wgsLat
    }
    if (dLng > 0) {
      pLng = wgsLng
    } else {
      mLng = wgsLng
    }

    if (++i > 10000) break
  }
  // console.log(i);
  return { 'lat': wgsLat, 'lng': wgsLng }
}

// GCJ-02 to BD-09
export function bd_encrypt(gcjLat, gcjLng) {
  const x = gcjLng
  var y = gcjLat
  const z = Math.sqrt(x * x + y * y) + 0.00002 * Math.sin(y * x_pi)
  const theta = Math.atan2(y, x) + 0.000003 * Math.cos(x * x_pi)
  const bdLng = z * Math.cos(theta) + 0.0065
  const bdLat = z * Math.sin(theta) + 0.006
  return { 'lat': bdLat, 'lng': bdLng }
}

// BD-09 to GCJ-02
export function bd_decrypt(bdLat, bdLng) {
  const x = bdLng - 0.0065
  var y = bdLat - 0.006
  const z = Math.sqrt(x * x + y * y) - 0.00002 * Math.sin(y * x_pi)
  const theta = Math.atan2(y, x) - 0.000003 * Math.cos(x * x_pi)
  const gcjLng = z * Math.cos(theta)
  const gcjLat = z * Math.sin(theta)
  return { 'lat': gcjLat, 'lng': gcjLng }
}

// WGS-84 to Web mercator
// mercatorLat -> y mercatorLng -> x
export function mercator_encrypt(wgsLat, wgsLng) {
  const x = wgsLng * 20037508.34 / 180.0
  let y = Math.log(Math.tan((90.0 + wgsLat) * PI / 360.0)) / (PI / 180.0)
  y = y * 20037508.34 / 180.0
  return { 'lat': y, 'lng': x }
  /*
   if ((Math.abs(wgsLng) > 180 || Math.abs(wgsLat) > 90))
   return null;
   var x = 6378137.0 * wgsLng * 0.017453292519943295;
   var a = wgsLat * 0.017453292519943295;
   var y = 3189068.5 * Math.log((1.0 + Math.sin(a)) / (1.0 - Math.sin(a)));
   return {'lat' : y, 'lng' : x};
   //*/
}

// Web mercator to WGS-84
// mercatorLat -> y mercatorLng -> x
export function mercator_decrypt(mercatorLat, mercatorLng) {
  const x = mercatorLng / 20037508.34 * 180.0
  let y = mercatorLat / 20037508.34 * 180.0
  y = 180 / PI * (2 * Math.atan(Math.exp(y * PI / 180.0)) - PI / 2)
  return { 'lat': y, 'lng': x }
  /*
   if (Math.abs(mercatorLng) < 180 && Math.abs(mercatorLat) < 90)
   return null;
   if ((Math.abs(mercatorLng) > 20037508.3427892) || (Math.abs(mercatorLat) > 20037508.3427892))
   return null;
   var a = mercatorLng / 6378137.0 * 57.295779513082323;
   var x = a - (Math.floor(((a + 180.0) / 360.0)) * 360.0);
   var y = (1.5707963267948966 - (2.0 * Math.atan(Math.exp((-1.0 * mercatorLat) / 6378137.0)))) * 57.295779513082323;
   return {'lat' : y, 'lng' : x};
   //*/
}

// two point's distance
export function distance(latA, lonA, latB, lonB) {
  const earthR = 6371000.0
  const x = Math.cos(latA * PI / 180.0) * Math.cos(latB * PI / 180.0) * Math.cos((lonA - lonB) * PI / 180)
  const y = Math.sin(latA * PI / 180.0) * Math.sin(latB * PI / 180.0)
  let s = x + y
  if (s > 1) s = 1
  if (s < -1) s = -1
  const alpha = Math.acos(s)
  const distance = alpha * earthR
  return distance
}

export function outOfChina(lat, lng) {
  if (lng < 72.004 || lng > 137.8347) {
    return true
  }
  if (lat < 0.8293 || lat > 55.8271) {
    return true
  }
  return false
}

export function transformLat(x, y) {
  let ret = -100.0 + 2.0 * x + 3.0 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * Math.sqrt(Math.abs(x))
  ret += (20.0 * Math.sin(6.0 * x * PI) + 20.0 * Math.sin(2.0 * x * PI)) * 2.0 / 3.0
  ret += (20.0 * Math.sin(y * PI) + 40.0 * Math.sin(y / 3.0 * PI)) * 2.0 / 3.0
  ret += (160.0 * Math.sin(y / 12.0 * PI) + 320 * Math.sin(y * PI / 30.0)) * 2.0 / 3.0
  return ret
}

export function transformLng(x, y) {
  let ret = 300.0 + x + 2.0 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * Math.sqrt(Math.abs(x))
  ret += (20.0 * Math.sin(6.0 * x * PI) + 20.0 * Math.sin(2.0 * x * PI)) * 2.0 / 3.0
  ret += (20.0 * Math.sin(x * PI) + 40.0 * Math.sin(x / 3.0 * PI)) * 2.0 / 3.0
  ret += (150.0 * Math.sin(x / 12.0 * PI) + 300.0 * Math.sin(x / 30.0 * PI)) * 2.0 / 3.0
  return ret
}
